During the coating of surfaces with curable resins or plastisols, as well as during the preparation of molded articles by pouring curable resins into molds and curing the resins in the molds, small gas bubbles, are frequently formed, which usually are finely dispersed in the organic phase. A portion of these bubbles floats to the surface of the lacquer or coating, bursts there and causes no disorders, as long as the flowability of the lacquer or plastisol film is still large enough to equalize or even out the disturbed surface by afterflow. Another portion of the bubbles rises to the surface, but does not burst there and, when the lacquer cures or the plastisols gels, forms a very thin surface skin which can easily be damaged mechanically. Other bubbles remain dispersed in the film or in the molded articles formed. Such disorders in a lacquer film are referred to as pinholes.
The phenomenon of this so-called microfoam is not to be compared with the behavior and appearance of a normal, more or less small-celled polyhedral foam. While the known defoamers or antifoamers destroy the partitions between the individual foam bubbles or prevent their stable formation, the individual, mostly spherical gas bubbles in microfoams of such water-dilutable coating systems are so far removed from one another, that no lamellae or partitions are formed between the individual spheres of foam. For this reason, the known antifoaming agents usually fail to eliminate and remove the microfoam. Such elimination or removal is also referred to as deaerating. Further references to the different behavior of spherical foam and polyhedral foam are given in "Ullmanns Encyclopadie der technischen Chemie" (Ullmann's Encyclopedia of Chemical Engineering) volume 20, pp. 441 ff.
It may be assumed that phenomena at the interface between the gas bubbles and the liquid affect the deaeration. Possibly, the deaeration is affected by changes in the viscosity of the coating system in the boundary surface to the gas bubbles. In any case, because of the different physical and/or chemical effects on the interfaces between the liquid and the gas, a person skilled in this art, knowing the effectiveness of antifoaming agents, is unable to draw reasonable conclusions concerning the effectiveness of so-called deaerating agents.